linux-kernel - [PATCH/RFC] remove irqs_disabled warning from local_bh

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Message-Id: <1213739834.3803.137.camel@johannes.berg>
Date:	Tue, 17 Jun 2008 23:57:14 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Linux Kernel list <linux-kernel@...r.kernel.org>
Cc:	Michael Buesch <mb@...sch.de>,
	David Ellingsworth <david@...ntd.dyndns.org>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH/RFC] remove irqs_disabled warning from local_bh_enable

This warning has started to trigger with mac80211 because it can, under
some circumstances, use spin_lock_bh() protected sections within
irq-disabled sections. Is that a bug?

Interestingly, the warning was never noticed until somebody ran the code
on UP/NO-PREEMPT because local_bh_enable_ip() does not contain such a
warning. Also, because softirq disabling is refcounted (via the preempt
counter), it ought to be safe to nest it and even use within
irqs-disabled sections, as far as I can tell.

Also, if you're going to treat IRQs being enabled as a bug, there's no
point in disabling them right afterwards, is there?

If you're going to reject this patch, I'll post one that adds the
warning to local_bh_enable_ip() to allow detecting this for everybody
and not just those poor people running UP/NO-PREEMPT :)

(and why doesn't local_bh_enable just call local_bh_enable_ip anyway? or
both "call" a common static inline?)
---
 kernel/softirq.c |    3 ---
 1 file changed, 3 deletions(-)

--- everything.orig/kernel/softirq.c	2008-06-17 23:48:25.000000000 +0200
+++ everything/kernel/softirq.c	2008-06-17 23:48:56.000000000 +0200
@@ -137,10 +137,7 @@ void local_bh_enable(void)
 	unsigned long flags;
 
 	WARN_ON_ONCE(in_irq());
-#endif
-	WARN_ON_ONCE(irqs_disabled());
 
-#ifdef CONFIG_TRACE_IRQFLAGS
 	local_irq_save(flags);
 #endif
 	/*


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